1. Field of Invention
This invention relates to a point of sale printer having an internally retained paper supply roll, and, more particularly, to such a printer having a paper supply roll rotatably mounted along a central axis of the paper roll, allowing the printer to operate in various orientations without causing the distortion of print lines due to variations in frictional resistance to paper movement.
2. Background Art
Point of sale printers, which are typically used to print receipts at cash registers, conventionally print on a web of paper extending from a paper supply roll, with the length of the document being printed being conveniently determined by separation of an individual document from the web following printing. Conventionally, the paper supply roll is installed within the printer by dropping it into a paper supply bucket having a support surface shaped as a section of a cylinder. The roll is held in place with its periphery on the support surface by gravity as the paper web is pulled from it and is allowed to rotate on the support surface. Idler rolls, against which the paper supply roll periphery turns, may be used to reduce the frictional loading retarding rotation of the paper supply roll.
One problem with this conventional approach to supporting a paper supply roll arises from the fact that gravity is used to hold the paper supply roll in a particular orientation. This reliance on gravity determines the orientation in which the printer should be placed to operate properly. For example, as long as the printer is resting essentially flat on a horizontal counter top, the direction of gravity can be relied upon to hold the paper supply roll in such a way that the paper web is pulled off the roll smoothly by a paper feed roll within the printer. On the other hand, in many retail establishments counter space suitable for holding a printer near a cash register is not readily available, so there is a desire to mount the printer somewhere else, such as on a vertical wall or otherwise on a shelf. When a conventional point of sale printer is mounted in an unconventional orientation, the paper supply roll does not rest in the support surface of the paper bucket in the normal way, so that the paper web may not pull smoothly from the paper supply roll. Even if the paper drive roll pulling the paper web from the paper supply roll is still able to move the paper web, variations in the frictional characteristics of the means for rotatably mounting the paper supply roll can cause the paper movement to be retarded or uneven, so that visible distortion occurs in the shapes of the characters being printed and in the space between lines of print.
Therefore, what is needed is a way to mount the paper supply roll in a manner which is not dependent on the direction of gravity, so that the printer can be mounted in various orientations according to the desires of the user.
Several U.S. Patents describe mechanisms for rotatably mounting a paper roll, such as a toilet paper roll, by engaging the inner tube of the roll. For example, U.S. Pat. No. 1,625,190 describes a method for mounting the tube to rotate on a pair of spherical bearings extending partly within each end of the cardboard tube. Each spherical bearing moves within a tapered aperture in a side plate and a housing extending outward from the side plate. With the spherical bearings in their lowest position, the spherical balls extend within the cardboard tube; as the balls are raised, they move outward into the housings. An advantage of this method for mounting a roll is that springs are not required to hold the parts in place. Disadvantages are that the roll must be installed in a downward direction and removed in an upward direction, and that the reliance on gravity to hold the roll in place means that the general orientation of the apparatus must be maintained.
U.S. Pat. Nos. 2,555,885 and 4,614,312 describe roll paper holders having with hollow plungers extending into the opposing ends of a tubular roll core. Coil springs extending within the plungers hold partially spherical portions in place within the core, and a flange extending outward from each of the partially spherical portions limits the angle through which a plunger can be tilted. The paper roll is inserted and removed by overcoming the forces exerted by the springs.
U.S. Pat. No. 5,228,633 describes apparatus for holding paper rolls in printing devices, e.g. facsimile machines, in which paper roll supports including conical portions extending into the central hole within a paper roll are urged inwardly by elastomeric foam pads extending between the paper roll supports and end plates.
U.S. Pat. No. 4,452,403 describes a dispenser for material, such as toilet paper, paper towels, or plastic wrap, arranged in a roll, with the dispenser including articulated end pieces that loosely engage the central opening of the roll and hold the roll in position for dispensing. The end pieces are pivotally attached to the frame and are spring biased to urge them into engaging positions. The potential use of such a dispenser in the different application of a paper supply mechanism of a printer is limited by the fact that the roll must be loosely held by flexibly mounted end pieces, providing room for such end pieces to flip into place within the central opening of the roll as the roll is slid into the dispenser. In the application of a paper supply for a printer, the roll should be more tightly held to provide for smooth operation and the keep the paper tracking straight along the paper path.
A further disadvantage in the devices described in U.S. Pat. Nos. 2,555,885, 4,452,402, 4,614,312, and 5,228,633 arises from the fact that the forces holding the plungers or end pieces in place are directly overcome to install or remove a roll being slid within the dispenser, while there is no mechanism to lock the roll within the dispenser when it is not being inserted or removed. Thus, pulling the paper from the dispenser hard enough during normal operation may dislodge the roll within the dispenser. Also, if the roll is mounted in a portable device, such as a point of sale printer, the roll may be dislodged by acceleration forces resulting from moving the device from one location to another.
U.S. Pat. No. 4,821,974 describes a paper roll supply assembly for a large document printer to permit simplified loading and unloading of a media roll. Two end support assemblies are mounted in an axial alignment position. Each end support assembly includes a spindle shaft, a hub assembly, and a coil compression spring. The paper roll support core is seated on tapered surfaces of the hub assemblies; the compression spring allows one end to be urged outward so that, once the media roll is fully seated against the hub assembly, one spring predominates and serves to maintain the roll in a precisely aligned axial position. Each of the tapered surfaces of the hub assemblies is divided into three sections to provide a space between tapered sections into which the paper roll may be pivoted and swung into place.
The assembly of U.S. Pat. No. 4,821,974 has an advantage over other prior art devices in that the hub assemblies are tapered at a low enough angle to prevent dislodging the paper roll as paper is pulled away from the roll or as the device of which the paper roll supply assembly is a part is moved. However, this assembly has a disadvantage of requiring a more difficult process for aligning the paper roll with the mounting hubs and for swinging the paper roll into place. The paper roll cannot merely be slid into place from any direction. Also, this assembly has a disadvantage or requiring much more space within the device for the loading process and for the springs and movable hub assemblies.
The IBM Technical Disclosure Bulletin, March, 1972, pp. 3115-3116, describes a dual-spindle support for rolled paper in which the spindles, facing one another when extending within opposing ends of a core within a paper roll, are mounted on hinged support flaps that are pivoted outward to release the paper roll. The support flaps are connected to links, which extend toward one another, and which are pivotally attached to a latch disk at diagonally opposite positions. The latch disk is rotated in a first direction to pivot the support flaps so that the spindles are moved into engagement with the paper roll and opposite the first direction to release the paper roll. The paper support mechanism is shown mounted within a drawer to be slid into a device, such as a copier.
The paper support mechanism thus described in the IBM Technical Disclosure Bulletin also has the advantage of latching the paper roll in place on the spindles so that it cannot be dislodged as paper is pulled away from the roll or as the device is moved. However, this mechanism has disadvantages of requiring a fairly complex additional mechanism to move the support flaps and of requiring substantial space within the device for movement of these flaps.
Thus, what is needed is a paper roll support mechanism latching the paper roll to be rotatably held in place during operation without the additional space requirements and complexity disadvantages of the mechanisms described in U.S. Pat. No. 4,821,974 and in the IBM Technical Disclosure Bulletin. 
According to one aspect of the present invention, apparatus is provided for mounting a paper supply roll within a printing device. The apparatus includes a paper supply frame, first and second bearing members, first inward and outward motion stops, and a first resilient member. The paper supply frame includes a cavity for holding the paper supply roll and first and second end walls extending along opposite ends of the cavity. The paper supply frame is movable within the printing device between an open position providing access for installation of the paper supply roll into the cavity and for removal of the paper supply roll from the cavity, and a closed position. A paper web is fed from the paper supply roll within the printing device with the paper supply frame in the closed position. The first bearing member, which engages a first end of the paper supply roll at a central hole of the paper supply, includes a first convex roll mounting surface extending into the cavity from the first end wall and is movably mounted within the first end wall to move inward and outward. The second bearing member, which engages a second end of the paper supply roll at the central hole of the paper supply roll, includes a second convex roll mounting surface extending into the cavity from the second end wall. The first inward motion stop limits inward movement of the first bearing member at the first end wall. The first outward motion stop limits outward motion of the first bearing member when the paper supply frame is in the closed position. Movement of the paper supply frame into the open position moves the first bearing member out of engagement with the first outward motion stop. The first resilient member pushes the first bearing member inward.
Preferably, the second bearing member is movably mounted within the second end wall to move inward and outward, with the apparatus additionally including second inward and outward motion stops and a second resilient member. The second inward motion stop limits inward movement of the second bearing member at the second end wall. The second outward motion stop limits outward motion of the second bearing member when the paper supply frame is in the closed position, Movement of the paper supply frame into the open position moves the second bearing member out of engagement with the second outward motion stop. The second resilient member pushes the second bearing member inward.
According to another aspect of the present invention conversion apparatus is provided for converting paper supply apparatus, holding a wide paper roll within a wide cavity between first and second bearing members extending inward from first and second end walls forming portions of a paper supply frame, the second bearing member being pushed inward in a first guide hole within the second end wall by a resilient member, to hold a narrow paper roll. The conversion apparatus includes an intermediate wall and a third bearing member. The intermediate wall, which is removably mounted to the paper supply frame within the wide cavity to form a narrow cavity between the first end wall and the intermediate wall, includes a second guide hole. The third bearing member has a convex roll mounting surface extending into the narrow cavity and an end opposite the convex roll mounting surface extending through the first guide hole to engage the resilient member.